1. Field of the Invention
The present invention relates to a surface-mountable circuit component suitably used in a portable information terminal, etc. that is required to have a small-size, high-density, and high-efficiency profile, a circuit component package, and a circuit component built-in module, as well as to methods for producing the circuit component package and the circuit component built-in module.
2. Related Background Art
Recently, with the reduction of size and the increase of the packaging density of electric and electronic apparatuses, a technique of providing a plurality of components as one package for each functional block in forming a module has been used often, as compared with the conventional technique of forming electric circuits by mounting individual component on a board. The module thus formed is formed usually by mounting necessary components on one side or both sides of a daughter board. However, with the method of mounting individual components on a surface of a board, it is impossible to make the module area smaller than the area of components mounted, and hence, there is a limit on the further increase in the packaging density. Further, in the case of this method, since the components are arranged planarly, connection distances between components necessarily increase according to the configurations of components arranged. This increases the resistance loss and causes a problem regarding the impedance match with respect to high frequencies.
Therefore, a configuration of a module in which components are arranged three-dimensionally has been proposed, in which components are not only mounted two-dimensionally on a surface of a board but also within the board. As a method for producing such a module, there are, for instance, a method of providing a gap in a ceramic substrate and arranging a component in the gap portion, and a method of providing a gap portion in a multi-layer printed circuit board and arranging a component in the gap portion.
However, in the case of the method of providing a gap in a ceramic substrate and arranging a component in the gap portion, it is impossible to incorporate a circuit component containing semiconductor or an organic substance in the substrate since the method involves a sintering process. Therefore, it is impossible to mount a component at a position above the portion where the gap is provided and the circuit component is arranged. This enables a low profile structure, but the three-dimensional arrangement of components is not applicable thereto actually. Therefore, there is a limit on the further increase of the packaging density by this method. Furthermore, in the case where a ceramic substrate is used, since the connection between layers is carried out through vias that are obtained by sintering a high-resistance metal such as tungsten and molybdenum, the connection resistance is relatively high. This is a significant problem as to power supply circuits that are adversely affected by losses.
On the other hand, in the case of the method of providing a gap in a multi-layer printed circuit board and arranging a component in the gap portion, the connection between layers with low resistances is enabled by through hole connection, but has difficulty with heat radiation since the printed circuit board has a low heat conductivity, thereby not allowing heat generated from the component arranged in the board to be transferred to the outside. Therefore, in an actual design, the temperature rise has to be taken into consideration, and this makes it impossible to arrange components at a higher density. Still further, the printed circuit board has a thermal expansion coefficient of approximately 60 ppm/° C. in the thickness direction, which significantly differs from a thermal expansion coefficient of copper as a material of plating (17 ppm/° C.). Therefore, there is also a problem in connection reliability.
JP 11-220262A discloses a circuit component built-in module with which high packaging density and high reliability can be achieved by solving the foregoing problems. The circuit component built-in module incorporates at least one active component and/or passive component in an electric insulation substrate made of a mixture containing at least an inorganic filler and a thermosetting resin, the inorganic filler being 70 percent by weight (wt %) to 95 wt %, and a plurality of wiring patterns arranged therein are connected electrically through inner vias made of a conductive resin composition. This circuit component built-in module makes it possible to arrange components at a higher density by the three-dimensional component arrangement, and provides a higher reliability due to the matching between thermal expansion coefficients.
A circuit component used in such a circuit component built-in module is a surface-mountable type principally. This is because it is important to arrange the components at a high density with respect to the board. When such surface-mountable components are mounted on a board, the components normally are mounted on wiring patterns arranged on the board, and electrode portions of the components and the wiring patterns are connected electrically using a solder or a conductive adhesive. FIG. 18 illustrates a state in which a surface mountable component 101 is mounted on a board 104 on which a wiring pattern 105 is provided. The circuit component 101 is composed of a component body 102, and external electrodes 103 provided at ends of the component body 102.
However, in the case where a normal surface-mountable circuit component is used, the external electrode portions at the ends thereof have a thickness slightly greater than a thickness of the component body. This is because when the external electrodes are formed, a metal paste or the like is applied on surfaces of the component body and sintered, and thereafter, plating films are formed further thereon, whereby the portions necessarily become thick. Therefore, as shown in FIG. 18, when the component is mounted on the substrate 104 on which the wiring pattern 105 is provided, a gap 106 is formed between the component body 102 of the circuit component 101 and a mounting member composed of the board 104 and the wiring pattern 105. The presence of the gap 106 causes a problem when the circuit component 101 is embedded in an electric insulation material so that a circuit component built-in module is produced, as the circuit component 101 cracks due to pressure applied thereto upon being embedded.
Further, in the process of embedding the circuit component connected with the wiring pattern in the electric insulation material, heating has to be carried out so as to cure the electric insulation material after the embedding. Therefore, in the case where the circuit component is connected with the wiring pattern with use of a low-melting metal such as a solder, when the temperature reaches the melting point of the low-melting metal in the heating process, the low-melting metal flows into the gap between the circuit component and the wiring pattern, thereby making a short-circuit.